linux-kernel - Re: [PATCH v12 09/26] x86/resctrl: Introduce interface to display number of monitoring counters

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Message-ID: <d9f58494-4561-47c6-b87b-44e2853bf910@amd.com>
Date: Mon, 14 Apr 2025 15:12:40 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, tony.luck@...el.com,
 peternewman@...gle.com
Cc: corbet@....net, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
 paulmck@...nel.org, akpm@...ux-foundation.org, thuth@...hat.com,
 rostedt@...dmis.org, ardb@...nel.org, gregkh@...uxfoundation.org,
 daniel.sneddon@...ux.intel.com, jpoimboe@...nel.org,
 alexandre.chartre@...cle.com, pawan.kumar.gupta@...ux.intel.com,
 thomas.lendacky@....com, perry.yuan@....com, seanjc@...gle.com,
 kai.huang@...el.com, xiaoyao.li@...el.com, kan.liang@...ux.intel.com,
 xin3.li@...el.com, ebiggers@...gle.com, xin@...or.com,
 sohil.mehta@...el.com, andrew.cooper3@...rix.com, mario.limonciello@....com,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 maciej.wieczor-retman@...el.com, eranian@...gle.com
Subject: Re: [PATCH v12 09/26] x86/resctrl: Introduce interface to display
 number of monitoring counters

Hi Reinette,

On 4/11/25 16:01, Reinette Chatre wrote:
> Hi Babu,
> 
> On 4/3/25 5:18 PM, Babu Moger wrote:
>> The mbm_cntr_assign mode provides an option to the user to assign a
>> counter to an RMID, event pair and monitor the bandwidth as long as
>> the counter is assigned. Number of assignments depend on number of
>> monitoring counters available.
>>
>> Provide the interface to display the number of monitoring counters
> 
> An interface can also be a function. To help make this work obvious
> it can be specific:
> 
> 	Create 'num_mbm_cntrs' resctrl file that displays the number of
> 	monitoring counters supported in each domain. 'num_mbm_cntrs'
> 	is only visible to user space when the system supports
> 	mbm_cntr_assign mode.

ok. Sure.

> 
>> supported in each domain. The resctrl file 'num_mbm_cntrs' is visible
>> to user space when the system supports mbm_cntr_assign mode.
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
> ...
> 
>> ---
>>  Documentation/arch/x86/resctrl.rst     | 11 ++++++++++
>>  arch/x86/kernel/cpu/resctrl/monitor.c  |  3 +++
>>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 30 ++++++++++++++++++++++++++
>>  3 files changed, 44 insertions(+)
>>
>> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
>> index bb96b44019fe..35d908befdfb 100644
>> --- a/Documentation/arch/x86/resctrl.rst
>> +++ b/Documentation/arch/x86/resctrl.rst
>> @@ -284,6 +284,17 @@ with the following files:
>>  	misleading values or display "Unavailable" if no counter is assigned
>>  	to the event.
>>  
>> +"num_mbm_cntrs":
>> +	The maximum number of monitoring counters (total of available and assigned
>> +	counters) in each domain when the system supports mbm_cntr_assign mode.
>> +
>> +	For example, on a system with maximum of 32 memory bandwidth monitoring
>> +	counters in each of its L3 domains:
>> +	::
>> +
>> +	  # cat /sys/fs/resctrl/info/L3_MON/num_mbm_cntrs
>> +	  0=32;1=32
>> +
>>  "max_threshold_occupancy":
>>  		Read/write file provides the largest value (in
>>  		bytes) at which a previously used LLC_occupancy
>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index 6ed7e51d3fdb..028b49878ad0 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -1234,6 +1234,9 @@ int __init resctrl_mon_resource_init(void)
>>  	else if (resctrl_arch_is_mbm_total_enabled())
>>  		mba_mbps_default_event = QOS_L3_MBM_TOTAL_EVENT_ID;
>>  
>> +	if (r->mon.mbm_cntr_assignable)
>> +		resctrl_file_fflags_init("num_mbm_cntrs", RFTYPE_MON_INFO);
> 
> Missing RFTYPE_RES_CACHE?


Please see my response here.

https://lore.kernel.org/lkml/4fc02936-237d-4060-86af-79efc28a72e5@amd.com/

> 
>> +
>>  	return 0;
>>  }
>>  
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index 626be6becca7..0c9d7a702b93 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -912,6 +912,30 @@ static int resctrl_mbm_assign_mode_show(struct kernfs_open_file *of,
>>  	return 0;
>>  }
>>  
>> +static int resctrl_num_mbm_cntrs_show(struct kernfs_open_file *of,
>> +				      struct seq_file *s, void *v)
>> +{
>> +	struct rdt_resource *r = of->kn->parent->priv;
>> +	struct rdt_mon_domain *dom;
>> +	bool sep = false;
>> +
>> +	cpus_read_lock();
>> +	mutex_lock(&rdtgroup_mutex);
>> +
>> +	list_for_each_entry(dom, &r->mon_domains, hdr.list) {
>> +		if (sep)
>> +			seq_puts(s, ";");
> 
> seq_putc() can be used.
> 
Sure.

>> +
>> +		seq_printf(s, "%d=%d", dom->hdr.id, r->mon.num_mbm_cntrs);
>> +		sep = true;
>> +	}
>> +	seq_puts(s, "\n");
> 
> seq_putc() can be used.

Sure.

> 
>> +
>> +	mutex_unlock(&rdtgroup_mutex);
>> +	cpus_read_unlock();
>> +	return 0;
>> +}
>> +
>>  #ifdef CONFIG_PROC_CPU_RESCTRL
>>  
>>  /*
>> @@ -1945,6 +1969,12 @@ static struct rftype res_common_files[] = {
>>  		.seq_show	= resctrl_mbm_assign_mode_show,
>>  		.fflags		= RFTYPE_MON_INFO,
>>  	},
>> +	{
>> +		.name		= "num_mbm_cntrs",
>> +		.mode		= 0444,
>> +		.kf_ops		= &rdtgroup_kf_single_ops,
>> +		.seq_show	= resctrl_num_mbm_cntrs_show,
>> +	},
>>  	{
>>  		.name		= "cpus",
>>  		.mode		= 0644,
> 
> Reinette
> 

-- 
Thanks
Babu Moger